Battery management architectures for flow batteries

ABSTRACT

Systems and methods for managing flow batteries utilize a battery management controller (BMC) coupled between a flow battery and a DC/DC converter, which is coupled to an electrical grid or a photovoltaic device via an inverter. The inverter converts an AC voltage to a first DC voltage and the DC/DC converter steps down the first DC voltage to a second DC voltage. The BMC includes a first power route, a second power route, and a current source converter coupled to the second power route. The BMC initializes the flow battery with a third DC voltage using the current source converter until a sensing circuit senses that the voltage of the flow battery has reached a predetermined voltage. The sensing circuit may include a capacitor, which has a small capacitance and is coupled across each cell of the flow battery, coupled in series between two resistors having very large resistances.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 62/682,481.

FIELD

The technology of this disclosure is generally related to managing flowbatteries, for example, in conjunction with electrical energy generationand distribution systems.

BACKGROUND

A flow battery is a type of electrochemical cell where chemical energyis provided by two chemical components dissolved in two respectiveliquids separated by a membrane. Ion exchange, which is accompanied byflow of electric current, occurs through the membrane while the twoliquids circulate in two respective volumes separated by the membrane.

A flow battery may be used like a rechargeable battery where an electricpower source drives regeneration of the fuel. Flow batteries provide avariety of advantages over conventional rechargeable batteries includinga flexible layout, a long cycle life, quick response times, and noharmful emissions. Because of these advantages, flow batteries may beused in a wide variety of applications. Such applications includestoring energy from renewable sources such as solar for discharge duringpeak demand periods and load balancing where the flow battery isconnected to an electrical grid to store excess electrical power duringoff-peak hours and release electrical power during peak demand periods.

SUMMARY

The techniques of this disclosure generally relate to managing flowbatteries.

In one aspect, this disclosure features a system including a flowbattery. The system also includes an inverter that converts an ACvoltage from an electrical grid or a photovoltaic device to a first DCvoltage. The system also includes a DC/DC converter coupled to theinverter. The DC/DC converter steps down the first DC voltage to asecond DC voltage. The system also includes a battery managementcontroller (BMC) coupled between the DC/DC converter and the flowbattery. The BMC including a first power route, a second power route inparallel with the first power route, and a current source convertercoupled to the second power route. The BMC initializes the flow batterywith a third DC voltage using the current source converter.

In aspects, implementations of this disclosure may include one or moreof the following features. The first DC voltage may range between 1200volts and 1400 volts. The second DC voltage may range between 40 voltsand 80 volts. The third DC voltage may range between 0 volts and 80volts. The photovoltaic device may be a solar tracker. The BMC mayinclude one or more power converters coupled to an output of the BMC.The BMC may include a semiconductor switch coupled to the first powerroute. The semiconductor switch may be turned off when the flow batteryis initialized with a third DC voltage using the current sourceconverter.

The BMC may include two switches coupled to respective terminals of theflow battery. The switches may switch between a connection to the firstpower route and a connection to the second power route. The two switchesmay switch to the connection to the second power route when the flowbattery is initialized with a third DC voltage using the current sourceconverter. The two switches may switch to the connection to the firstpower route when a voltage of the flow battery reaches a predeterminedvoltage. The predetermined voltage may be between 40 V and 65 V.

The system may also include multiple sensing circuits that sensevoltages of multiple cells of the flow battery. Each sensing circuit ofthe sensing circuits may include a first resistor having a very largeresistance, a capacitor having a small capacitance, and a secondresistor having a very large resistance coupled in series between avoltage rail and ground. The capacitor may be connected across contactsof a cell of the multiple cells of the flow battery. The very largeresistance may be between 1 Mohm and 10 Mohm. The small capacitance maybe between 1 μF and 0.01 μF. The flow battery may be a vanadium, ironchromium, zinc bromine, or zinc iron flow battery.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the techniques described in this disclosurewill be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of this disclosure are described herein below withreference to the drawings, which are incorporated in and constitute apart of this specification, wherein:

FIG. 1 is a block diagram of one aspect of the disclosed system;

FIG. 2 is a graphical diagram of voltage and current operatingcharacteristics of one aspect of a vanadium flow battery;

FIG. 3 is a block diagram of one aspect of certain components in thebattery management controller (BMC) of FIG. 1;

FIG. 4 is a block diagram of another aspect of the BMC of FIG. 1; and

FIG. 5 is a circuit diagram of a sensing circuit for sensing the voltageof a cell in a flow battery stack.

DETAILED DESCRIPTION

A system, architecture, and method are disclosed for integrating a solartracker, a battery, an inverter, and a battery management controller toimprove performance and costs. The system may incorporate a flowbattery, such as an advanced vanadium flow battery (VFB). Thisdisclosure provides an architecture that optimizes performance forcommercial, industrial, agricultural, and utility applications, amongother applications.

This disclosure relates to systems and architectures for seamlesslyintegrating solar systems, e.g., solar tracker systems, with flowbatteries, such as vanadium flow batteries. Aspects of such systems aredisclosed in, for example, U.S. Provisional Patent Application No.62/667,129, filed May 4, 2018, and U.S. Provisional Patent ApplicationNo. 62/667,960, filed May 7, 2018, the entire contents of each of whichare hereby incorporated by reference herein.

The system of this disclosure includes a battery management controller(BMC) to provide flow battery system control. In various aspects, theresponsibility of the BMC includes providing power to all necessaryfunctions to operate the vanadium flow battery.

FIG. 1 is a diagram of one aspect of the disclosed system, whichincludes a flow battery 102, a battery management controller (BMC) 104,a DC/DC converter 106, and an inverter 108. The inverter 108 can becoupled to an electrical grid 112, such as an industrial electrical gridthat can provide, for example, 480 VAC, and/or to photovoltaics (PV)input 114.

The flow battery 102 will be described in more detail below herein.Generally, when the flow battery 102 is being initialized, thecomponents 102, 104, 106, 108 of FIG. 1 operate from right to left. Thatis, power is provided from the electrical grid 112 and/or the PV input114. The inverter 108 converts the AC voltage from the electrical grid112 to a first DC voltage, for example, 1200-1400 VDC, and the DC/DCconverter 106 steps down the DC voltage, to, for example, between 40-80VDC. The BMC 104 uses this voltage to initialize the flow battery 102.This operation is described in more detail in connection with FIG. 3. Inthe illustrated aspect, the voltage at the terminals of the flow battery102 can range between 0 and 80 volts.

The vanadium flow battery 102 allows the charge and discharge to takeplace entirely in the liquid phase. Since the energy is stored in liquidform, the batteries can effectively manage the heat that is generatedinside the flow battery 102 during the charge-discharge cycle, thuspreventing the possibility of accidental overheating and prolonging theservice life. However, because the VFB energy is in liquid form, a pumpis needed to move the liquid to generate voltage and current.

VFB systems have fewer components and have lower cost of ownership. VFBsare designed so that they do not degrade over the life cycle of thesystem. With conventional batteries, the electrodes degrade with eachcharge-discharge cycle, and the cells lose performance over time andmust be replaced. VFBs, however, can generally operate as long as theapplication with which the VFBs are integrated—e.g., for 30 years ormore in solar plants.

VFBs are also flexible. Because of the separation of the cells andelectrolytes, the VFBs can be designed for either power or energyapplications. As more flow battery cell stacks are added, the power isincreased. Also, as the electrolyte tanks are enlarged, more energy isprovided.

FIG. 2 is a graphical diagram of voltage and current operatingcharacteristics of a vanadium flow battery. A VFB has a battery initialcharge phase 201 and an operating phase 202. As mentioned above,movement of the VFB liquid generates the voltage and current. Withoutsuch VFB liquid movement initially, the initial voltage of the VFB maybe as low as 0 VDC. The battery initial charge phase 201 of FIG. 2illustrates that current is needed to increase the voltage of the VFBthrough the battery initial charge phase 201 to reach the operatingphase 202. Thus, during the battery initial charge phase 201, the powerflow in FIG. 1 flows from right to left, and power is obtained from theelectrical grid 112 or PV device 114.

In the illustrated aspect, when the VFB voltage reaches about 40V, nofurther increase in current is needed to further increase the voltagethrough the battery initial charge phase 201 and reach the operatingphase 202. Once the VFB reaches the operating phase 202, the VFB 102 canpower the BMC 104, which operates to control the operation of the VFB102. In various aspects, at least 24 V is needed to power the BMC 104and for the BMC 104 to control operation of the flow battery 102.

FIG. 3 is a diagram of one aspect of certain components in the batterymanagement controller 104 of FIG. 1. The left-side terminals 311, 312connect to the VFB 102, and the right-side terminals 321, 322 connect tothe DC/DC converter 106 of FIG. 1. A current source converter 302outputs current with a voltage as low as 0V to initialize the flowbattery 102 during the battery initial charge phase 201. The BMC 104also includes one or more power converters 304 to provide the variousvoltage and current needs of the BMC 104.

The BMC 204 include two selectable power busses or routes—one powerroute 323 corresponding to the normal charge-discharge phase 202 and theother power route 324 corresponding to the battery initial charge phase201. In aspects, the power routes 323, 324 may be implemented by powerbuses or any suitable electrical conductors for carrying power betweenthe VFB 102 and the DC/DC converter 106.

When the VFB 102 is at the initial charge phase 201, the current sourceconverter 302 is enabled and is connected to the VFB 102 by operatingswitches 313, 314 so that the switches 313, 314 connect to power route324. In this mode, power from the electrical grid 112 or PV device 114,depending on PV device availability, flows into the right side of theBMC 104 and powers the current source converter 302, and the currentsource converter 302 is used to initialize the VFB 102. In this mode,the power converters 304 in the BMC 104 use the power from theelectrical grid and/or PV device to power the BMC 104.

Once the initial charge phase 201 is completed, the current sourceconverter 302 is disabled and is disconnected from the VFB by operatingswitches 313, 314 so that the switches 313, 314 disconnect from powerroute 324 and connect to power route 323. In various aspects, thecurrent source converter 302 can be disabled when the voltage of the VFB102 reaches about 40-65 V in the battery initial charge phase 201. TheVFB 102 is then directly connected to the DC/DC converter 106. In thismode, the VFB 102 can be charged or can discharge and provide power tothe electrical grid 112. In this operating mode, for example, the VFB102 can be charged by energy from solar trackers via the PV input 114,or the VFB 102 can discharge to provide energy to the electrical grid112. Depending on whether the VFB 102 is charging or discharging, thepower converters 302 within the BMC 104 may be powered by differentenergy sources.

FIG. 4 shows another aspect of the BMC 104 of FIG. 1. When the VFB 102is in the battery initial charge phase 201, the current source converteris enabled and the semiconductor switch 402, which may be ametal-oxide-semiconductor field-effect transistor (MOSFET) or any othersuitable transistor, is turned off. Once the battery initial chargephase 201 is completed, the current source converter 302 is disabled andsemiconductor switch 402 is turned on so that the VFB 102 is directlyconnected to the DC/DC converter 106. In various aspects, thesemiconductor switch 402 can be turned on when the voltage of the VFB102 reaches about 40-65V in the battery initial charge phase 201.

The architecture and components of FIGS. 1, 3, and 4, may not need anadditional power supply to power the BMC 104 or an additional converterto operate the VFB 102.

FIG. 5 shows a sensing circuit 500 for sensing the voltage of a cell ina flow battery stack. The sensing circuit 500 can measure one cell ofthe VFB 102 through electrical contacts or terminals 501, 502 to sensethe state of charge, and this measurement can be used by the BMC 104 tocontrol the VFB 102. In various aspects, the sensing circuit 500 can beincluded in the BMC 104. In various aspects, the sensing circuit 500 canbe outside the BMC 104 but can be connected to the BMC 104.

The sensing circuit 500 includes a voltage rail 504 that can provide asmall voltage, for example, 3.3 VDC. The voltage at the voltage rail 504can be provided by a power converter, e.g., one of the power converters302, in the BMC 104, which may be an isolated power supply. The sensingcircuit 500 also includes a ground connection 506. Connected between thevoltage rail 504 and the ground connection 506 are, in series, a verylarge resistance 511, a small capacitance 510, and another very largeresistance 512. In the illustrated aspect, the very large resistances511, 512 are 1 Mohm and the small capacitance 510 is 0.1 μF. Othervalues and combinations of resistances and capacitances are contemplatedto be within the scope of this disclosure. For example, the very largeresistances of the resistors 511, 512 can be in the range of about 1Mohm to 10 Mohm, and the capacitance of the capacitor 510 can be in therange of about 1 μF to 0.01 μF.

When the sensing circuit is disconnected from a VFB cell, the voltageacross the capacitor may be 3.3 VDC. When the sensing circuit 500 isthen connected to the VFB cell, the voltage across the capacitor 510will decrease to the voltage of the VFB cell, which is typically in therange of −0.6 to 1.6 VDC. During this transition, a small amount ofcurrent flows into the VFB cell. Additionally, when the voltage acrossthe capacitor 510 is less than 3.3VDC, a small amount of current flowsthrough the resistors 511, 512 corresponding to the voltage difference,and this small amount of current also flows through the VFB cell. Whenthe voltage across the capacitor 510 reaches the voltage of the VFBcell, no current is provided by the capacitor 510, but a small currentcontinues to flow through the resistors 511, 512 and through the VFBcell. Because the resistances of the resistors 511, 512 are very large,the current flowing through the resistors 511, 512 would be very smalland would not perturb the VFB cell. For example, in the illustratedaspect of FIG. 5, the maximum current flow can be(3.3−(−0.6))/1000000=0.0000039=3.9 uA.

The sensing circuit 500 configured in the illustrated aspect can detectthe voltage range of a typical VFB cell, which can be in the range of−0.6 to 1.6 VDC, while not disturbing the VFB cell. Additionally, thesensing circuit 500 can be used to detect that the VFB 102 isdisconnected because the voltage across the capacitor would be about 3.3VDC.

While several aspects of the disclosure have been shown in the drawings,it is not intended that the disclosure be limited thereto, as it isintended that the disclosure be as broad in scope as the art will allowand that the specification be read likewise. Any combination of theabove aspects is also envisioned and is within the scope of the appendedclaims. Therefore, the above description should not be construed aslimiting, but merely as exemplifications of particular aspects. Thoseskilled in the art will envision other modifications within the scope ofthe claims appended hereto.

Although the description above refers to a vanadium flow battery, othertypes of flow batteries can be used with the present disclosure. Forexample, flow batteries having other chemistries, including withoutlimitation iron chromium, zinc bromine, or zinc iron, can be used inthis disclosure. The flow batteries can also be redox, hybrid, ormembraneless flow batteries.

What is claimed is:
 1. A system comprising: a flow battery; an inverterconfigured to convert an AC voltage from an electrical grid or aphotovoltaic device to a first DC voltage; a DC/DC converter coupled tothe inverter and configured to step down the first DC voltage to asecond DC voltage; and a battery management controller (BMC) coupledbetween the DC/DC converter and the flow battery, the BMC including afirst power route, a second power route in parallel with the first powerroute, and a current source converter coupled to the second power route,the BMC being configured to initialize the flow battery with a third DCvoltage using the current source converter.
 2. The system of claim 1,wherein the first DC voltage ranges between 1200 volts and 1400 volts.3. The system of claim 1, wherein the second DC voltage ranges between40 volts and 80 volts.
 4. The system of claim 1, wherein the third DCvoltage ranges between 0 volts and 80 volts.
 5. The system of claim 1,wherein the photovoltaic device is a solar tracker.
 6. The system ofclaim 1, wherein the BMC includes one or more power converters coupledto an output of the BMC.
 7. The system of claim 1, wherein the BMCincludes a semiconductor switch coupled to the first power route, andwherein the semiconductor switch is turned off when the flow battery isinitialized with the third DC voltage using the current sourceconverter.
 8. The system of claim 1, wherein the BMC includes twoswitches coupled to respective terminals of the flow battery andconfigured to switch between a connection to the first power route and aconnection to the second power route, and wherein the two switches areconfigured to switch to the connection to the second power route whenthe flow battery is initialized with a third DC voltage using thecurrent source converter.
 9. The system of claim 8, wherein the twoswitches are configured to switch to the connection to the first powerroute when a voltage of the flow battery reaches a predeterminedvoltage.
 10. The system of claim 9, wherein the predetermined voltage isbetween 40 V and 65 V.
 11. The system of claim 9, further comprising aplurality of sensing circuits configured to sense a voltage of arespective plurality of cells of the flow battery, wherein each sensingcircuit of the plurality of sensing circuits includes a first resistorhaving a very large resistance, a capacitor having a small capacitance,and a second resistor having a very large resistance coupled in seriesbetween a voltage rail and ground, wherein the capacitor is coupledacross contacts of a cell of the plurality of cells of the flow battery.12. The system of claim 11, wherein the very large resistance is between1 Mohm and 10 Mohm.
 13. The system of claim 11, wherein the smallcapacitance is between 1 μF and 0.01 μF.
 14. The system of claim 1,wherein the flow battery is a vanadium, iron chromium, zinc bromine, orzinc iron flow battery.